1. Field of the Invention
The present invention relates to an optical waveguide fox a touch panel and a touch panel using the same.
2. Description of the Related Art
Touch panels are input devices for operating an apparatus by directly touching a display screen of a liquid crystal display device or the like with a finger, a purpose-built stylus or the like, and include a display which displays operation details and the like, and a detection means which detects the position (coordinates) of a portion of the display screen of the display touched with the finger or the like. Information about the touch position detected by the detection means is sent in the form of a signal to the apparatus, which in turn performs an operation and the like displayed on the touch position. Examples of the apparatus employing such a touch panel include ATMs in banking facilities, ticket vending machines in stations, portable game machines, and the like.
A detection means employing an optical waveguide is proposed as the detection means for detecting the finger touch position and the like on the above-mentioned touch panel (see, for example, U.S. 2004/0201579A1). Specifically, the touch panel includes optical waveguides provided around a periphery of a display screen of a rectangular display, and is configured to emit a multiplicity of light beams parallel to the display screen of the display from an optical waveguide provided on one side portion of the display screen toward the other side portion, and to cause the light beams to enter an optical waveguide provided on the other side portion. These optical waveguides cause the light beams to travel in a lattice form on the display screen of the display. When a portion of the display screen of the display is touched with a finger in this state, the finger blocks some of the light beams. Therefore, the light-receiving optical waveguide senses a light blocked portion, whereby the position of the portion touched with the finger is detected.
The light beams emitted from an optical waveguide directly into the air diverge radially. There has been proposed a light-emitting optical waveguide including a core having an end portion formed in a lens-shaped configuration so as to suppress the divergence of the emitted light beams (see, for example, U.S. 2005/0089298A1).
For a touch panel using the above-mentioned optical waveguides, it is necessary that the light beams emitted from the light-emitting optical waveguide into the air be incident on the core of the light-receiving optical waveguide. In this case, when the emitted light beams spread too wide, there is a low probability that the light beans enter the core of the light-receiving optical waveguide, which results in low optical transmission efficiency. To overcome such a problem, it is contemplated to form an end portion of the core in a lens-shaped configuration to narrow down the emitted light beams by the use of the technique disclosed in U.S. 2005/0089298A1 described above. However, narrowing down the emitted light beams reduces the size of a light-receiving region too much and makes it difficult for the core of the light-receiving optical waveguide to receive the light beams (or makes it impossible for the core of the light-receiving optical waveguide to receive the light beams if the core of the light-receiving optical waveguide is deviated from its proper position even slightly).